The invention relates to a steering spindle arrangement and to a method for producing it.
A steering spindle arrangement of generic type and a production method of the generic type are disclosed in German Patent Document No. DE-A 14 30 946. The arrangement which is described comprises two telescopic steering spindle components which are fixed frictionally on each other, with the steering moment transmitted by the steering wheel to the inner component being passed on to the outer spindle component by the frictional connection. If there is an axial impact in the event of a crash, the two components are pushed one inside the other, with impact energy being consumed by the friction. The frictional connection is formed in different ways, namely, first, by means of a tolerance ring which is arranged in a groove on the inner circumference of the outer component and, secondly by a plastic layer which is placed in the plug-in position of the components and imparts the frictional connection between the components. As a further variant, those ends of the components which communicate with each other have spring-loaded form-fitting elements which are provided with bevels, engage one inside the other and, in the use position of the components, are caused by the compression spring to slide on the bevels in such a manner that a radial pressing of the inner component against the outer component is produced. In addition, those ends of the components which are connected to each other are locked in a form-fitting manner in the circumferential direction by means of their polygonal shape, as a result of which the steering torque can be transmitted even better.
However, one disadvantage of the known arrangement is that the arrangement of a tolerance ring is relatively complicated, since the latter has to be specially adapted to the cross-sectional dimensioning of the outer steering spindle component and requires a securing device (receiving groove) which complicates the production of the steering spindle. Furthermore, the tolerance ring itself has manufacturing tolerances which, in comparison to the individual steering spindles, result in the travel of the inner component being dispersed and therefore to different levels of energy absorption in vehicle collisions. This means that—contrary to the required safety conditions—it is not possible to establish a specific, uniform safety standard for the steering spindle from the outset. The plastic-layer variant shown is less practicable, since the plastic layer wears very rapidly and over time transmits the steering moment very imprecisely to the outer component, which results in a risk to the driver. In addition, the method for producing the frictional connection with the layer is awkward, since the layer has to be placed over a very narrow annular gap between the spindle components. This means a method step for producing the connection, in which it cannot be assessed whether the layer is completely formed and can thus provide the expected frictional connection level. The other variant having the bevelled form-fitting elements is also very complicated in terms of the design and installation. In addition, in a crash the driver might be subjected to a spontaneous, unbraked impact, since the form-fitting element of the other component is fastened to it and thus prevents displacement of the inner component.
The invention is based on the object of developing a generic arrangement to the effect that, in a simple manner, as specific a definition as possible of the absorption by the steering spindle of the deformation energy in the event of a crash is obtained while ensuring that the arrangement is durable and directly transmits the steering moment. Furthermore, it is the object of the invention to develop a generic method for producing the arrangement to the effect that it can be carried out with only a little outlay and reliably.
Owing to the invention, all of the structural elements which impart the frictional connection between the inner and outer steering spindle components are omitted in the arrangement. This simplifies the construction of the arrangement on account of the reduction in the number of parts. Furthermore, no manufacturing tolerances and/or wear of the structural elements arise, with the result that a specific definition of the absorption by the steering spindle of the deformation energy in the event of a crash is possible. The press fit produced by pressing together the two steering spindle components can be reliably produced with little outlay by various methods, for example by magnetic pulse deformation or thermal shrinking-on of the outer component in the plug-in position of the two components. The direct contact of the component walls against each other results in direct transfer by the arrangement of the steering moment. The press fit furthermore ensures that the arrangement is durable in normal operation and is able, owing to the high frictional force of the joining partners, i.e., the two steering spindle components, to absorb large displacement forces in the event of a crash. The frictional connection can be set in a specific manner by selecting the process parameters of the production methods, with it being possible for a certain axial displacement force to be established for a crash situation and hence for a uniform force profile to be produced. This selection enables the force profile to be varied as desired in accordance with requirements.